The statistics of particle velocities in dense granular flows

TL;DR

This study measures particle velocity distributions in dense granular flows, revealing non-Gaussian, anisotropic, and power-law behaviors, with surprising uniformity across different flow regions and implications for understanding granular dynamics.

Contribution

It provides detailed measurements of velocity distributions in dense granular flows, highlighting their non-Gaussian and anisotropic nature, and challenges existing hydrodynamic theories.

Findings

Velocity distribution is non-Gaussian and anisotropic.

Distribution follows a power law at large velocities.

Velocity variance peaks at the core, contrary to predictions.

Abstract

We present measurements of the particle velocity distribution in the flow of granular material through vertical channels. Our study is confined to dense, slow flows where the material shears like a fluid only in thin layers adjacent to the walls, while a large core moves without continuous deformation, like a solid. We find the velocity distribution to be non-Gaussian, anisotropic, and to follow a power law at large velocities. Remarkably, the distribution is identical in the fluid-like and solid-like regions. The velocity variance is maximum at the core, defying predictions of hydrodynamic theories. We show evidence of spatially correlated motion, and propose a mechanism for the generation of fluctuational motion in the absence of shear.